Tire Mold and Pneumatic Tire

ABSTRACT

A tire mold comprises sector molds for forming a tread portion of a tire and mold pins provided on the sector molds for forming insertion holes in the tread portion. The insertion holes each comprise a first hole portion with a first inner diameter where a body portion of a stud pin is disposed and a second hole portion with a second inner diameter greater than the first inner diameter where a bottom flange portion of the stud pin is disposed. The mold pins each comprise a trunk portion with a first outer diameter for forming the first hole portion and a tip portion with a second outer diameter greater than the first outer diameter for forming the second hole portion.

TECHNICAL FIELD

The present technology relates to a tire mold and a pneumatic tire.

BACKGROUND ART

Known winter tires include studded tires that include stud pins. Studpins are inserted in insertion holes provided in the tread portion ofthe tire. Japanese Patent No. 5513345B describes a studded tiremanufactured via the steps including vulcanizing a green tire in a moldthat includes projection portions that include mold pins, removing thevulcanized tire from the mold, and inserting the stud pins into theinsertion holes formed in the tire by the projection portions. The moldincludes a plurality of sector molds that form the tread portion of thetire and side molds that form the sidewall portions of the tire. Theprojection portions for forming the insertion holes are provided onsector molds.

SUMMARY

After vulcanization of a tire, cracks can form in the region around theinsertion holes, caused when the projection portions are removed fromthe insertion holes. Such cracks can cause the holding force that holdsthe stud pins in the insertion holes to be decreased, spoil theappearance of the tire, and cause the performance of the studded tire tobe decreased.

An aspect of the present technology has an object of providing a tiremold and a pneumatic tire capable of suppressing cracking when forminginsertion holes.

A first aspect of the present technology provides a tire mold forforming a tire that includes insertion holes into which stud pins areinserted, the tire mold comprising:

a plurality of sector molds for forming a tread portion of the tire, theplurality of sector molds being disposed in a tire circumferentialdirection; and

a plurality of mold pins for forming the insertion holes in the treadportion, the plurality of mold pins being provided on inner surfaces ofthe plurality of sector molds that oppose the tread portion andprojecting inward in a tire radial direction;

the stud pins each comprising a body portion and a bottom flangeportion;

the insertion holes each comprising a first hole portion with a firstinner diameter where the body portion of the stud pin is disposed and asecond hole portion with a second inner diameter greater than the firstinner diameter where the bottom flange portion of the stud pin isdisposed;

the plurality of mold pins each comprising a trunk portion with a firstouter diameter for forming the first hole portion and a tip portion witha second outer diameter greater than the first outer diameter forforming the second hole portion; and

the first outer diameter of the trunk portion of an end mold pin of theplurality of mold pins provided in an end region in the tirecircumferential direction of each of the plurality of sector molds beinggreater than the first outer diameter of the trunk portion of a middlemold pin of the plurality of mold pins provided in a middle region ofeach of the plurality of sector molds, the middle region being locatedbetween the end region on one side and the end region on the other sidein the tire circumferential direction.

According to the first aspect of the present technology, the first outerdiameter of the end mold pin is greater than the first outer diameter ofthe middle mold pin. As a result, when the sector molds are movedoutward in the tire radial direction to release the tire and the endmold pins are removed from the insertion holes formed in the tire,cracking caused by removal of the end mold pins is suppressed.

The angle formed by the movement axis of the sector mold and the centeraxis of the middle mold pin is small when the sector molds are movedoutward in the tire radial direction. The angle formed by the movementaxis of the sector mold and the center axis of the end mold pin islarge.

The first outer diameter of the trunk portion of the mold pin beingsmall includes in its meaning the difference between the first outerdiameter of the trunk portion of the mold pin and the second outerdiameter of the tip portion of the mold pin being great. The first outerdiameter of the trunk portion of the mold pin being large includes inits meaning the difference between the first outer diameter of the trunkportion of the mold pin and the second outer diameter of the tip portionof the mold pin being small.

If the difference between the first outer diameter and the second outerdiameter of the end mold pin having a center axis that forms a largeangle with the movement axis of the sector mold is great, when the endmold pin is removed from the insertion hole, the stress acting upon therubber in a region around the insertion hole is great. As a result,cracking is highly likely to occur in a region around the insertionhole.

By the first outer diameter of the trunk portion of the end mold pinbeing great and the difference between the first outer diameter of thetrunk portion of the end mold pin and the second outer diameter of thetip portion of the end mold pin being small, even when the end mold pinwith a center axis that forms a large angle with the movement axis ofthe sector mold is removed from the insertion hole, the stress actingupon the rubber in a region around the insertion hole is suppressed. Asa result, cracking in regions around the insertion holes formed by theend mold pins is suppressed.

The first outer diameter of the middle mold pin is small and thedifference between the first outer diameter and the second outerdiameter of the middle mold pin is greater, however the angle formed bythe center axis of the middle mold pin and the movement axis of thesector mold is small. As a result, when the middle mold pin is removedfrom the insertion hole, the stress acting upon the rubber in a regionaround the insertion hole is suppressed. Accordingly, cracking inregions around the insertion holes formed by the middle mold pins issuppressed.

By suppressing cracking, a decrease in the holding force of the studpins provided by the insertion holes and spoiling of the appearance ofthe studded tire, which are caused by such cracking, can be prevented.Thus, a decrease in the performance of the studded tire is prevented.

Additionally, according to the first aspect of the present technology,the mold pin comprising the trunk portion with the first outer diameterand the tip portion with the second outer diameter has a circular shapein a plane orthogonal to the center axis of the mold pin. Accordingly,in the installation of the mold pins into the sector molds, excessiveattention does not need to be paid to the orientation of the mold pinswith respect to the rotation direction about the center axis. Thus,complexity of the labor involved is suppressed. Additionally, crackingconditions changing due to the orientation of the mold pin issuppressed.

In the first aspect of the present technology, a difference between thefirst outer diameter of the end mold pin and the first outer diameter ofthe middle mold pin may be from 0.1 mm to 1.0 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.1 mm, cracking in a region aroundthe insertion hole formed by the end mold pin may not be sufficientlysuppressed. If the difference is greater than 1.0 mm, the holding forceof the stud pin provided by the insertion hole formed by the end moldpin is likely to decrease.

In the first aspect of the present technology, the second outer diameterof the tip portion of the end mold pin may be less than the second outerdiameter of the tip portion of the middle mold pin.

This effectively suppresses crack and thus maintains the performance ofthe studded tire. The second outer diameter of the tip portion of themold pin being great includes in its meaning the difference between thefirst outer diameter of the trunk portion of the mold pin and the secondouter diameter of the tip portion of the mold pin being small. Thesecond outer diameter of the tip portion of the mold pin being smallincludes in its meaning the difference between the first outer diameterof the trunk portion of the mold pin and the second outer diameter ofthe tip portion of the mold pin being large. By the second outerdiameter of the tip portion of the end mold pin being small and thedifference between the first outer diameter of the trunk portion of theend mold pin and the second outer diameter of the tip portion of the endmold pin being small, even when the end mold pin with a center axis thatforms a large angle with the movement axis of the sector mold is removedfrom the insertion hole, the stress acting upon the rubber in a regionaround the insertion hole is suppressed. As a result, cracking inregions around the insertion holes formed by the end mold pins issuppressed.

In the first aspect of the present technology, a difference between thesecond outer diameter of the end mold pin and the second outer diameterof the middle mold pin may be from 0.2 mm to 1.5 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.2 mm, cracking in a region aroundthe insertion hole formed by the end mold pin may not be sufficientlysuppressed. If the difference is greater than 1.5 mm, the holding forceof the stud pin provided by the insertion hole formed by the end moldpin is likely to decrease.

In the first aspect of the present technology, a length of the end moldpin may be less than a length of the middle mold pin.

As a result, cracking is effectively suppressed. By the length of theend mold pin being small, even when the end mold pin with a center axisthat forms a large angle with the movement axis of the sector mold isremoved from the insertion hole, the stress acting upon the rubber in aregion around the insertion hole is suppressed.

As a result, cracking in regions around the insertion holes formed bythe end mold pins is suppressed.

In the first aspect of the present technology, a difference between thelength of the end mold pin and the length of the middle mold pin may befrom 0.1 mm to 1.0 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.1 mm, cracking in a region aroundthe insertion hole formed by the end mold pin may not be sufficientlysuppressed. If the difference is greater than 1.0 mm, the holding forceof the stud pin provided by the insertion hole formed by the end moldpin is likely to decrease.

In the first aspect of the present technology, the end mold pin may be amold pin of the plurality of mold pins provided on each of the pluralityof sector molds located closest to an end portion of the sector mold inthe tire circumferential direction.

As a result, cracking in a region around the insertion hole formed bythe end mold pin with a center axis that forms the greatest angle withthe movement axis of the sector mold is suppressed.

In the first aspect of the present technology,

the tread portion may comprises a first region on one side of an equatorline of the tire in a tire lateral direction and a second region on theother side,

the plurality of mold pins may comprise a plurality of mold pins forforming the insertion holes in the first region and a plurality of moldpins for forming the insertion holes in the second region, and

the end mold pin may be a mold pin of the plurality of mold pins forforming the insertion holes in the first region and the second regionlocated closest to an end portion of each of the plurality of sectormolds in the tire circumferential direction.

As a result, cracking in a region around the insertion holes formed inthe first region and cracking in a region around the insertion holesformed in the second region are suppressed. Thus, the stud pins in thefirst region and the second region are prevented from falling out and adecrease in the running performance of the studded tire is suppressed.

In the first aspect of the present technology, the middle mold pin maybe a mold pin of the plurality of mold pins provided on the plurality ofsector molds other than the end mold pins, and the first outer diameter,the second outer diameter, and the length may be the same for all of themiddle mold pins.

As a result, it is sufficient to prepare only two types of mold pins,the end mold pin and the middle mold pin, thus suppressing the cost ofthe tire mold.

A second aspect of the present technology provides a pneumatic tire,comprising:

a tread portion formed by a plurality of sector molds disposed in a tirecircumferential direction;

a plurality of insertion holes into which stud pins are inserted, theplurality of insertion holes being formed in the tread portion by moldpins provided on inner surfaces of the plurality of sector molds thatoppose the tread portion and projecting inward in a tire radialdirection;

the stud pins each comprising a body portion and a bottom flangeportion;

the plurality of insertion holes each comprising a first hole portionwith a first inner diameter where the body portion of the stud pin isdisposed and a second hole portion with a second inner diameter greaterthan the first inner diameter where the bottom flange portion of thestud pin is disposed; and

the first inner diameter of the first hole portion of an end insertionhole of the plurality of insertion holes formed in an end region in thetire circumferential direction of a predetermined region, which isformed by one of the plurality of sector molds, of the tread portionbeing greater than the first inner diameter of the first hole portion ofa middle insertion hole of the plurality of insertion holes formed in amiddle region of the tread portion, the middle region being locatedbetween the end region on one side and the end region on the other sidein the tire circumferential direction.

According to the second aspect of the present technology, the firstinner diameter of the end insertion hole is greater than the first innerdiameter of the middle insertion hole. As a result, when the sectormolds are moved outward in the tire radial direction to release the tireand the mold pins are removed from the insertion holes formed in thetire, cracking caused by removal of the mold pins is suppressed. Thus, adecrease in the performance of the pneumatic tire is prevented.

Additionally, according to the second aspect of the present technology,the insertion hole comprising the first hole portion with the firstinner diameter and the second hole portion with the second innerdiameter has a circular shape in a plane orthogonal to the center axisof the insertion hole. Accordingly, in forming the insertion holes,excessive attention does not need to be paid to the orientation of theinsertion holes with respect to the rotation direction about the centeraxis. Thus, complexity of the labor involved is suppressed.Additionally, cracking conditions changing due to the orientation of theinsertion hole is suppressed.

In the second aspect of the present technology, a difference between thefirst inner diameter of the end insertion hole and the first innerdiameter of the middle insertion hole may be from 0.1 mm to 1.0 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.1 mm, cracking in a region aroundthe end insertion hole may not be sufficiently suppressed. If thedifference is greater than 1.0 mm, the holding force of the stud pinprovided by the end insertion hole is likely to decrease.

In the second aspect of the present technology, the second innerdiameter of the second hole portion of the end insertion hole may beless than the second inner diameter of the second hole portion of themiddle insertion hole.

As a result, cracking is more effectively suppressed.

In the second aspect of the present technology, a difference between thesecond inner diameter of the end insertion hole and the second innerdiameter of the middle insertion hole may be from 0.2 mm to 1.5 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.2 mm, cracking in a region aroundthe end insertion hole may not be sufficiently suppressed. If thedifference is greater than 1.5 mm, the holding force of the stud pinprovided by the end insertion hole is likely to decrease.

In the second aspect of the present technology, a length of the endinsertion hole may be less than a length of the middle insertion hole.

As a result, cracking is effectively suppressed.

In the second aspect of the present technology, a difference between thelength of the end insertion hole and the length of the middle insertionhole may be from 0.1 mm to 1.0 mm.

This suppresses crack and thus maintains the performance of the studdedtire. If the difference is less than 0.1 mm, cracking in a region aroundthe end insertion hole may not be sufficiently suppressed. If thedifference is greater than 1.0 mm, the holding force of the stud pinprovided by the end insertion hole is likely to decrease.

In the second aspect of the present technology, the end insertion holemay be an insertion hole of the plurality of insertion holes provided inthe predetermined region located closest to an end portion of thepredetermined region in the tire circumferential direction.

As a result, cracking in a region around the end insertion hole with acenter axis that forms the greatest angle with the movement axis of thesector mold is suppressed.

In the second aspect of the present technology, the tread portion maycomprise a first region on one side of a tire equator line in a tirelateral direction and a second region on the other side,

the plurality of insertion holes may be formed in the first region andthe second region, and the end insertion hole may be an insertion holeof the plurality of insertion holes formed in the first region locatedclosest to an end portion of the predetermined region in the tirecircumferential direction and may be an insertion hole of the pluralityof insertion holes formed in the second region located closest to an endportion of the predetermined region in the tire circumferentialdirection.

As a result, cracking in a region around the insertion holes formed inthe first region and cracking in a region around the insertion holesformed in the second region are suppressed. Thus, the stud pins in thefirst region and the second region are prevented from falling out and adecrease in the running performance of the studded tire is suppressed.

In the second aspect of the present technology, the middle insertionhole may be an insertion hole of the plurality of insertion holesprovided in the tread portion other than the end mold pins, and

the first inner diameter, the second inner diameter, and the length maybe the same for all of the middle insertion holes.

As a result, it is sufficient to prepare only two types of insertionholes, the end insertion hole and the middle insertion hole, thussuppressing the cost of the pneumatic tire.

An aspect of the present technology provides a tire mold and a pneumatictire capable of suppressing cracking in a region around insertion holes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a portion ofa mold according to a first embodiment.

FIG. 2 is a diagram schematically illustrating an example of theoperation of the mold according to the first embodiment.

FIG. 3 is diagram schematically illustrating an example of a sector moldaccording to the first embodiment.

FIG. 4 is diagram schematically illustrating an example of a mold pinaccording to the first embodiment.

FIG. 5 is diagram schematically illustrating an example of the operationof the sector mold according to the first embodiment.

FIG. 6 is a cross-sectional view schematically illustrating an exampleof the insertion holes according to the first embodiment.

FIG. 7 is a side view illustrating an example of a stud pin according tothe first embodiment.

FIG. 8 is a side view illustrating an example of the stud pin and theinsertion hole according to the first embodiment.

FIG. 9 is a cross-sectional view illustrating an example of a studdedtire according to the first embodiment.

FIG. 10 is a plan view illustrating an example of the studded tireaccording to the first embodiment.

FIG. 11 is a diagram schematically illustrating an example of a treadportion of a studded tire according to a second embodiment.

FIG. 12 is a table showing results of evaluation tests for theconventional example and examples.

DETAILED DESCRIPTION

Embodiments according to the present technology will be described withreference to the appended drawings. However, the present technology isnot limited to these embodiments. Constituents of the embodimentsdescribed below can be combined with one another as appropriate. Inaddition, some of the constituents may not be used in some cases.

First Embodiment

A first embodiment will now be described. FIG. 1 is a cross-sectionalview schematically illustrating a portion of a tire mold 50 according tothe present embodiment. FIG. 2 is a diagram schematically illustratingan example of the operation of the mold 50 according to the presentembodiment.

The mold 50 forms a tire 1B that includes insertion holes 40 into whichstud pins are inserted. The mold 50 is a vulcanization mold. A greentire is disposed inside the mold 50. The green tire is supported by themold 50 when vulcanized.

The mold 50 includes a plurality of sector molds 51 for forming a treadportion 3 of the tire 1B disposed in the tire circumferential direction,and side molds 52 for forming sidewall portions 5 of the tire 1B.

Additionally, the mold 50 includes a plurality of mold pins 60 forforming the insertion holes 40 in the tread portion 3. The mold pins 60are disposed on an inner surface 53 of each of the sector molds 51 thatopposes the tread portion 3 of the tire 1B and project inward in thetire radial direction.

The tread portion 3 is formed by the plurality of sector molds 51disposed in the tire circumferential direction. The plurality ofinsertion holes 40 into which the stud pins are inserted are formed inthe tread portion 3 by the mold pins 60. The mold pins 60 are disposedon the inner surface 53 of each of the sector molds 51 that opposes thetread portion 3 and project inward in the tire radial direction.

Note that, although not illustrated, the sector molds 51 include aplurality of projection portions for forming grooves in the treadportion 3. A tread pattern is formed in the tire 1B by the projectionportions provided on the inner surface 53 of each of the sector molds51.

The side molds 52 include an upper side mold 52A and a lower side mold52B. The tire 1B is disposed between the upper side mold 52A and thelower side mold 52B.

As illustrated in FIG. 2, the sector molds 51 are arranged in the tirecircumferential direction. In the example illustrated in FIG. 2, themold 50 includes nine sector molds 51.

The sector molds 51 are members of an annular mold divided in the tirecircumferential direction. As illustrated by the arrow in FIG. 2, thesector molds 51 are moveable in the tire radial direction. The sectormolds 51 are brought into contact with the tread portion 3 of the tire1B by being moved inward in the tire radial direction. The sector molds51 are released from the tread portion 3 of the tire 1B by being movedoutward in the tire radial direction. The sector molds 51 move inward inthe tire radial direction to form an integrated annular mold. The sectormolds 51 move outward in the tire radial direction to become divided.

Note that FIG. 2 illustrates an example in which the annular mold isdivided into nine sections, i.e. includes nine sector molds 51. Theannular mold may be divided into eight sections, for example.

The upper side mold 52A is released from the sidewall portion 5 of thetire 1B by being moved upward. The upper side mold 52A is brought intocontact with the sidewall portion 5 of the tire 1B by being moveddownward. The lower side mold 52B is released from the sidewall portion5 of the tire 1B by being moved downward. The lower side mold 52B isbrought into contact with the sidewall portion 5 of the tire 1B by beingmoved upward.

FIG. 3 is diagram schematically illustrating an example of a sector mold51 according to the present embodiment. The sector mold 51 includes themold pins 60 arranged in the tire circumferential direction. The moldpins 60 include end mold pins 60A and middle mold pins 60B. The end moldpins 60A are provided in end regions 51A of the inner surface 53 of thesector mold 51 with respect to the tire circumferential direction. Themiddle mold pins 60B are provided in a middle region 51B of the innersurface 53 of the sector mold 51 between the end regions 51A.

Each end region 51A is a region spanning in the tire circumferentialdirection from the end portion of the inner surface 53 of the sectormold 51 to a position located a predetermined distance from the endportion toward the center of the inner surface 53. The end regions 51Ainclude the end region 51A that includes the end portion on one side ofthe inner surface 53 and the end region 51A that includes the endportion on the other side of the inner surface 53, with respect to thetire circumferential direction. The middle region 51B is the region ofthe inner surface 53 between the end region 51A on one side and the endregion 51A on the other side.

In the present embodiment, the end mold pins 60A are the mold pins 60provided on the sector mold 51 that are located closest to the endportions of the sector mold 51 with respect to the tire circumferentialdirection. In other words, among the mold pins 60 disposed in the tirecircumferential direction, the mold pin 60 located closest to the endportion on one side of the inner surface 53 and the mold pin 60 locatedclosest to the end portion on the other side of the inner surface 53 areend mold pins 60A. One sector mold 51 includes two end mold pins 60A.

The middle mold pins 60B are the mold pins 60 other than the end moldpins 60A provided on the sector mold 51. For example, in a configurationin which one sector mold 51 includes 32 mold pins 60, of the 32 moldpins 60, two are end mold pins 60A and 30 are middle mold pins 60B.

FIG. 4 is diagram schematically illustrating an example of the end moldpin 60A and the middle mold pin 60B according to the present embodiment.As illustrated in FIG. 4, the end mold pin 60A and the middle mold pin60B both include a base portion 63 connected to the inner surface 53 ofthe sector mold 51, a trunk portion 61 connected to the base portion 63,and a tip portion 62 connected to the trunk portion 61.

The end mold pin 60A is disposed about a center axis J60 a. In a planeorthogonal to the center axis J60 a, the base portion 63, the trunkportion 61, and the tip portion 62 of the end mold pin 60A have acircular shape. The center axis J60 a conforms with a radial axis fromthe center of the annular mold formed by the plurality of sector molds51.

The middle mold pin 60B is disposed about a center axis J60 b. In aplane orthogonal to the center axis J60 b, the base portion 63, thetrunk portion 61, and the tip portion 62 of the middle mold pin 60B havea circular shape. The center axis J60 b conforms with a radial axis fromthe center of the annular mold formed by the plurality of sector molds51.

The base portion 63 decreases in diameter as a distance from the theinner surface 53 increases. The trunk portion 61 has a cylindricalshape. The tip portion 62 increases in diameter as a distance from thefrom the inner surface 53 increases.

A first outer diameter D61 a that represents the dimensions of the trunkportion 61 of the end mold pin 60A in a plane orthogonal to the centeraxis J60 a is less than a second outer diameter D62 a that representsthe dimensions of the tip portion 62 of the end mold pin 60A. In otherwords, the second outer diameter D62 a is greater than the first outerdiameter D61 a. A first outer diameter D61 b that represents thedimensions of the trunk portion 61 of the middle mold pin 60B in a planeorthogonal to the center axis J60 b is less than a second outer diameterD62 b that represents the dimensions of the tip portion 62 of the middlemold pin 60B. In other words, the second outer diameter D62 b is greaterthan the first outer diameter D61 b.

A first length H61 a that represents the dimensions of the trunk portion61 of the end mold pin 60A in a plane parallel with the center axis J60a is greater than a second length H62 a that represents the dimensionsof the tip portion 62 of the end mold pin 60A. A first length H61 b thatrepresents the dimensions of the trunk portion 61 of the middle mold pin60B in a plane parallel with the center axis J60 b is greater than asecond length H62 b that represents the dimensions of the tip portion 62of the middle mold pin 60B.

In the present embodiment, the first outer diameter D61 a of the trunkportion 61 of the end mold pin 60A is greater than the first outerdiameter D61 b of the trunk portion 61 of the middle mold pin 60B. Inother words, the trunk portion 61 of the end mold pin 60A is thickerthan the trunk portion 61 of the middle mold pin 60B.

The difference between the first outer diameter D61 a of the end moldpin 60A and the first outer diameter D61 b of the middle mold pin 60B isfrom 0.1 mm to 1.0 mm.

The first outer diameter D61 a of the end mold pin 60A is, for example,from 2.0 mm to 2.4 mm. The first outer diameter D61 b of the middle moldpin 60B is from 0.1 mm to 1.0 mm less than the first outer diameter D61a.

Note that the difference between the first outer diameter D61 a and thefirst outer diameter D61 b is preferably from 0.2 mm to 0.5 mm.

In the present embodiment, the second outer diameter D62 a of the tipportion 62 of the end mold pin 60A is less than the second outerdiameter D62 b of the tip portion 62 of the middle mold pin 60B. Inother words, the tip portion 62 of the end mold pin 60A is thinner thanthe tip portion 62 of the middle mold pin 60B.

The difference between the second outer diameter D62 a of the end moldpin 60A and the second outer diameter D62 b of the middle mold pin 60Bis from 0.2 mm to 1.5 mm.

The second outer diameter D62 a of the end mold pin 60A is, for example,from 3.5 mm to 4.5 mm. The second outer diameter D62 b of the middlemold pin 60B is from 0.2 mm to 1.5 mm less than the second outerdiameter D62 a.

Note that the difference between the second outer diameter D62 a and thesecond outer diameter D62 b preferably is from 0.5 mm to 1.0 mm.

The difference Δa between the first outer diameter D61 a and the secondouter diameter D62 a of the end mold pin 60A is less than the differenceΔb between the first outer diameter D61 b and the second outer diameterD62 b of the middle mold pin 60B.

In the present embodiment, a length H60 a of the end mold pin 60A isless than a length H60 b of the middle mold pin 60B. The length H60 a isthe distance in the tire radial direction, which is parallel with thecenter axis J60 a, from the boundary portion between the inner surface53 of the sector mold 51 and the end mold pin 60A to the tip portion 62of the end mold pin 60A. The length H60 b is the distance in the tireradial direction, which is parallel with the center axis J60 b, from theboundary portion between the inner surface 53 of the sector mold 51 andthe middle mold pin 60B to the tip portion 62 of the middle mold pin60B.

The difference between the length H60 a of the end mold pin 60A and thelength H60 b of the middle mold pin 60B is from 0.1 mm to 1.0 mm.

The length H60 a of the end mold pin 60A is, for example, from 9.0 mm to10.0 mm. The length H60 b of the middle mold pin 60B is from 0.1 mm to1.0 mm greater than the length H60 a.

Note that the difference between the length H60 a and the length H60 bpreferably is from 0.1 mm to 0.5 mm.

In the present embodiment, the first length H61 a of the end mold pin60A is less than the first length H61 b of the middle mold pin 60B. Thesecond length H62 a of the end mold pin 60A may be equal to the secondlength H62 b of the middle mold pin 60B or may be less than the secondlength H62 b.

In the present embodiment, the first outer diameter D61 b, the secondouter diameter D62 b, and the length H60 b are the same for theplurality of middle mold pins 60B (for example, 30).

Next, an example of a method of manufacturing a studded tire 1 using amold 50 according to the present embodiment is described.

First, the mold 50 including the sector molds 51 and the side molds 52is prepared. The step of preparing the sector molds 51 includesinstalling the mold pins 60, which includes the end mold pins 60A andthe middle mold pins 60B, into the sector molds 51. In the presentembodiment, the end mold pins 60A have a circular shape in a planeorthogonal to the center axis J60 a, and the middle mold pins 60B have acircular shape in a plane orthogonal to the center axis J60 b.Accordingly, in the installation of the mold pins 60 into the sectormolds 51, excessive attention does not need to be paid to theorientation of the mold pins 60 with respect to the rotation directionabout the center axis J60.

The mold 50 is formed by assembling the sector molds 51 and the sidemolds 52 together. Adjacent sector molds 51 are brought in contact witheach other.

A green tire is disposed inside the mold 50. The sector molds 51 arebrought in contact with the tread portion 3 of the green tire. The sidemolds 52 are brought in contact with the sidewall portions 5 of thegreen tire. The insertion holes 40 are formed in the tread portion 3 bythe sector molds 51 that include the mold pins 60. The green tiredisposed inside the mold 50 is vulcanized by being subjected to highheat and pressure. The vulcanization forms the tire 1B that includes thetread portion 3 in which the insertion holes 40 are formed.

After vulcanization molding, the vulcanized tire 1B is removed from themold 50. The step of removing the tire 1B from the mold 50 includesreleasing the tire 1B by moving the sector molds 51 that are in contactwith the tire 1B outward in the tire radial direction.

FIG. 5 is a diagram schematically illustrating how the mold pins 60 areremoved from the insertion holes 40. As illustrated in FIG. 5, thesector molds 51 are moved outward in the tire radial direction toseparate from the tire 1B, causing the mold pins 60 to be removed fromthe insertion holes 40 formed in the tread portion 3 of the tire 1B.

The sector molds 51 move along a movement axis MX parallel with theradiation direction from the center axis of the tire 1B (the center axisof the annular mold). An angle θb between the movement axis MX of thesector mold 51 and the center axis J60 b of the middle mold pin 60B isless than an angle θa between the movement axis MX of the sector mold 51and the center axis J60 a of the end mold pin 60A.

In the present embodiment, the first outer diameter D61 a of the trunkportion 61 of the end mold pin 60A is greater than the first outerdiameter D61 b of the trunk portion 61 of the middle mold pin 60B. Thedifference Δa between the first outer diameter D61 a of the trunkportion 61 and the second outer diameter D62 a of the tip portion 62 ofthe end mold pin 60A is less than the difference Δb between the firstouter diameter D61 b of the trunk portion 61 and the second outerdiameter D62 b of the tip portion 62 of the middle mold pin 60B.

Thus, even when the end mold pin 60A with the center axis J60 a thatforms a large angle θa with the movement axis MX is removed from theinsertion hole 40, the stress acting upon a tread rubber 15 in a regionaround the insertion hole 40 is suppressed. Accordingly, cracking inregions around the insertion holes 40 formed by the end mold pins 60A issuppressed.

The first outer diameter D61 b of the middle mold pin 60B is less thanthe first outer diameter D61 a of the end mold pin 60A. The differenceΔb between the first outer diameter D61 b and the second outer diameterD62 b of the middle mold pin 60B is greater than the difference Δabetween the first outer diameter D61 a and the second outer diameter D62a of the end mold pin 60A. The angle θb between the center axis J60 b ofthe middle mold pin 60B and the movement axis MX of the sector mold 51is less than the angle θa between the center axis J60 a of the end moldpin 60A and the movement axis MX of the sector mold 51. Thus, when themiddle mold pin 60B is removed from the insertion hole 40, the stressacting upon the tread rubber 15 in a region around the insertion hole 40is suppressed. Accordingly, cracking in regions around the insertionholes 40 formed by the middle mold pins 60B is suppressed.

FIG. 6 is a cross-sectional view schematically illustrating an exampleof the insertion holes 40 according to the present embodiment. Theinsertion holes 40 are formed by the mold pins 60. The insertion holes40 include end insertion holes 40A formed by the end mold pins 60A andmiddle insertion holes 40B formed by the middle mold pins 60B.

As illustrated in FIG. 6, the end insertion hole 40A and the middleinsertion hole 40B both include a first hole portion 41 formed by thetrunk portion 61 of the mold pin 60, a second hole portion 42 formed bythe tip portion 62, and a third hole portion 43 formed by the baseportion 63. The trunk portion 61 forms the first hole portion 41. Thetip portion 62 forms the second hole portion 42.

The end insertion hole 40A is disposed about a center axis J40 a. In aplane orthogonal to the center axis J40 a, the first hole portion 41,the second hole portion 42, and the third hole portion 43 of the endinsertion hole 40A have a circular shape. The center axis J40 a conformswith a radial axis from the center of the tire 1B.

The middle insertion hole 40B is disposed about a center axis J40 b. Ina plane orthogonal to the center axis J40 b, the first hole portion 41,the second hole portion 42, and the third hole portion 43 of the middleinsertion hole 40B have a circular shape. The center axis J40 b conformswith a radial axis from the center of the tire 1B.

The third hole portion 43 decreases in diameter as away from a contactpatch 2 of the tread portion 3. The first hole portion 41 has acylindrical shape. The second hole portion 42 increases in diameter asaway from the contact patch 2.

A first inner diameter D41 a that represents the dimensions of the firsthole portion 41 of the end insertion hole 40A in a plane orthogonal tothe center axis J40 a is less than a second inner diameter D42 a thatrepresents the dimensions of the second hole portion 42 of the endinsertion hole 40A. In other words, the second inner diameter D42 a isgreater than the first inner diameter D41 a. A first inner diameter D41b that represents the dimensions of the first hole portion 41 of themiddle insertion hole 40B in a plane orthogonal to the center axis J40 bis less than a second inner diameter D42 b that represents thedimensions of the second hole portion 42 of the middle insertion hole40B. In other words, the second inner diameter D42 b is greater than thefirst inner diameter D41 b.

A first length H41 a that represents the dimensions of the first holeportion 41 of the end insertion hole 40A in a plane parallel with thecenter axis J40 a is greater than a second length H42 a that representsthe dimensions of the second hole portion 42 of the end insertion hole40A. A first length H41 b that represents the dimensions of the firsthole portion 41 of the middle insertion hole 40B in a plane parallelwith the center axis J40 b is greater than a second length H42 b thatrepresents the dimensions of the second hole portion 42 of the middleinsertion hole 40B.

In the present embodiment, the first inner diameter D41 a of the firsthole portion 41 of the end insertion hole 40A is greater than the firstinner diameter D41 b of the first hole portion 41 of the middleinsertion hole 40B. In other words, the first hole portion 41 of the endinsertion hole 40A is larger than the first hole portion 41 of themiddle insertion hole 40B.

The difference between the first inner diameter D41 a of the endinsertion hole 40A and the first inner diameter D41 b of the middleinsertion hole 40B is from 0.1 mm to 1.0 mm.

Note that the difference between the first inner diameter D41 a and thefirst inner diameter D41 b preferably is from 0.2 mm to 0.5 mm.

In the present embodiment, the second inner diameter D42 a of the secondhole portion 42 of the end insertion hole 40A is less than the secondinner diameter D42 b of the second hole portion 42 of the middleinsertion hole 40B. In other words, the second hole portion 42 of theend insertion hole 40A is thinner than the second hole portion 42 of themiddle insertion hole 40B.

The difference between the second inner diameter D42 a of the endinsertion hole 40A and the second inner diameter D42 b of the middleinsertion hole 40B is from 0.2 mm to 1.5 mm.

Note that the difference between the second inner diameter D42 a and thesecond inner diameter D42 b preferably is from 0.5 mm to 1.0 mm.

A difference Δc between the first inner diameter D41 a and the secondinner diameter D42 a of the end insertion hole 40A is less than adifference Δd between the first inner diameter D41 b and the secondinner diameter D42 b of the middle insertion hole 40B.

In the present embodiment, a length H40 a of the end insertion hole 40Ais less than a length H40 b of the middle insertion hole 40B. The lengthH40 a is the distance in the tire radial direction, which is parallelwith the center axis J40 a, from the contact patch 2 to the bottomsurface of the second hole portion 42 of the end insertion hole 40A. Thelength H40 b is the distance in the tire radial direction, which isparallel with the center axis J40 b, from the contact patch 2 to thebottom surface of the second hole portion 42 of the middle insertionhole 40B.

The difference between the length H40 a of the end insertion hole 40Aand the length H40 b of the middle insertion hole 40B is from 0.1 mm to1.0 mm.

Note that the difference between the length H40 a and the length H40 bpreferably is from 0.1 mm to 0.5 mm.

In the present embodiment, the first length H41 a of the end insertionhole 40A is less than the first length H41 b of the middle insertionhole 40B. The second length H42 a of the end insertion hole 40A may beequal to the second length H42 b of the middle insertion hole 40B or maybe less than the second length H42 b.

FIG. 7 is a side view illustrating an example of a stud pin 30 accordingto the present embodiment. FIG. 8 is a cross-sectional view illustratingan example of the stud pin 30 inserted into the insertion hole 40.

As illustrated in FIGS. 7 and 8, the stud pin 30 includes a body portion31, a bottom flange portion 32, and a tip portion 35. The body portion31 is supported by the bottom flange portion 32. The tip portion 35 issupported by the body portion 31. The bottom flange portion 32 and thebody portion 31 are disposed in the insertion hole 40 provided in thetread portion 3. The tip portion 35 is disposed in a manner so as toproject from the contact patch 2 of the tread portion 3.

In the present embodiment, the body portion 31 includes an upper flangeportion 33 and a middle portion 34. The body portion 31 and the bottomflange portion 32 are integrated (one member).

The stud pin 30 is disposed is a region around a center axis J30 thatpasses through the tip portion 35. In a plane orthogonal to the centeraxis J30, the body portion 31, the bottom flange portion 32, and the tipportion 35 have a circular shape. In other words, in the presentembodiment, the stud pin 30 is a circular pin. The bottom flange portion32 and the upper flange portion 33 are circular flanges. The middleportion 34 has a cylindrical shape.

An outer diameter D34 that represents the dimensions of the middleportion 34 in a plane orthogonal to the center axis J30 is less than anouter diameter D33 of the upper flange portion 33. The outer diameterD34 of the middle portion 34 is less than an outer diameter D32 of thebottom flange portion 32. The outer diameter D33 of the upper flangeportion 33 is less than the outer diameter D32 of the bottom flangeportion 32.

A height H34 that represents the dimensions of the middle portion 34 ina plane parallel with the center axis J30 is less than a height H33 ofthe upper flange portion 33. The height H34 of the middle portion 34 isgreater than a height H32 of the bottom flange portion 32. The heightH33 of the upper flange portion 33 is greater than the height H32 of thebottom flange portion 32.

As illustrated in FIG. 8, the body portion 31 of the stud pin 30 isdisposed in the first hole portion 41 of the insertion hole 40. Thebottom flange portion 32 of the stud pin 30 is disposed in the secondhole portion 42 of the insertion hole 40.

FIG. 9 is a cross-sectional view illustrating a portion of the studdedtire 1 according to the present embodiment. FIG. 9 illustrates ameridian cross-section passing through a rotation axis AX of the studdedtire 1. FIG. 10 is a plan view illustrating an example of the treadportion 3 of the studded tire 1 according to the present embodiment.

The studded tire 1 rotates about the rotation axis AX. The tirecircumferential direction includes the tire rotation direction about therotation axis AX. The tire lateral direction includes the directionparallel with the rotation axis AX. The tire radial direction includesthe radiation direction from the rotation axis AX. An equator line CL ofthe studded tire 1 is the center line which passes through the center ofthe studded tire 1 in the tire lateral direction.

The studded tire 1 is a winter tire (snow tire) provided with the studpins 30. The studded tire 1 may also be referred to as a spike tire 1.

The studded tire 1 includes the tire 1B and the stud pins 30 provided inthe tread portion 3 of the tire 1B. The tire 1B is a pneumatic tire. Thestud pins 30 are inserted into the insertion holes 40 formed in thetread portion 3.

As illustrated in FIG. 9, the tire 1B includes the contact patch 2, thetread portion 3 formed by the plurality of sector molds 51 disposed inthe tire circumferential direction, and the plurality of insertion holes40 formed in the tread portion 3 by the mold pins 60 disposed on theinner surface 53 of each of the sector molds 51 that opposes the treadportion 3 and project inward in the tire radial direction. The stud pins30 are inserted into the insertion holes 40.

Additionally, the tire 1B includes bead portions 4 that connect to therim and sidewall portions 5 that join the tread portion 3 and the beadportions 4. The contact patch 2 comes into contact with the road surface(ground) when the tire 1 runs.

The tire 1B includes a carcass 6 and an innerliner 7. The carcass 6 isthe framework of the tire 1B and maintains the shape of the tire 1B. Theinnerliner 7 is disposed facing the cavity of the tire 1B. The carcass 6and the innerliner 7 are disposed in the tread portion 3, the beadportions 4, and the sidewall portions 5.

The bead portions 4 each include a bead core 11 and a bead filler 12.The bead cores 11 fix the tire 1 to the rim. The bead cores 11 aredisposed on either side of the equator line CL of the tire 1B in thetire lateral direction. The bead cores 11 include a plurality ofhigh-carbon steel annular members bundled together. The bead cores 11are disposed so as to surround the rotation axis AX. The bead fillers 12increase the rigidity of the bead portions 4.

The tread portion 3 includes a belt 14 and the tread rubber 15. The belt14 includes a layer of belt members. The belt 14 is disposed on theouter side of the carcass 6 in the tire radial direction. The belt 14secures the carcass 6 and increases the rigidity of the tread portion 3.A tread pattern is formed in the tread rubber 15. The tread rubber 15 isdisposed on the outer side of the carcass 6 and the belt 14 in theradial direction. The contact patch 2 is disposed in the tread rubber15.

The sidewall portions 5 each include a sidewall rubber 16. The sidewallportions 5 are disposed on either side of the equator line CL in thetire lateral direction.

The carcass 6 is disposed in a toroidal form between the bead cores 11on either side of the equator line CL in the tire lateral direction. Thecarcass 6 is folded back at both end portions so as to surround the beadfillers 12.

Grooves 20 are formed in the tread rubber 15. The tread pattern isformed by the grooves 20. The grooves 20 include main grooves 21 formedin the tire circumferential direction and lug grooves 22 formed in thetire lateral direction (see FIG. 10). The tread rubber 15 is defined bythe main grooves 21 and the lug grooves 22, thus forming blocks 23. Thecontact patch 2 includes the surfaces of the blocks 23.

The studded tire 1 is provided with stud pins 30. The tire 1B includes aplurality of insertion holes 40 into which the stud pins 30 areinserted. The insertion holes 40 are formed in the tread portion 3 ofthe tire 1B. The insertion holes 40 are formed in the blocks 23 of thetread rubber 15. The stud pins 30 are at least partially disposed in theinsertion holes 40. The stud pins 30 are supported by the inner surfaceof the insertion holes 40 so as to partially project from the contactpatch 2 of the tread portion 3.

As illustrated in FIG. 10, the tread portion 3 includes a plurality ofinsertion holes 40 in the tire circumferential direction. The insertionholes 40 include the end insertion holes 40A provided in end regions 73Ain the tire circumferential direction of a predetermined region 73 ofthe tread portion 3 formed by one sector mold 51, and the middleinsertion holes 40B formed in a middle region 73B of the tread portion 3between the end region 73A on one side and the end region 73A on theother side.

The predetermined region 73 is a region formed by the contact of onesector mold 51. A boundary portion 70 between two adjacent predeterminedregions 73 opposes the boundary portion of two adjacent sector molds 51.The end portions of the predetermined regions 73 in the tirecircumferential direction include the boundary portion 70.

A line (protrusion portion) can form in the tread portion 3 due to a gapbetween two adjacent sector molds 51. In the vulcanization, the rubbercan enter the gap between two adjacent sector molds 51 and form a line.The boundary portion 70 may include such a line of rubber.

Each end region 73A is a region spanning in the tire circumferentialdirection from the end portion of the predetermined region 73 to aposition located a predetermined distance from the end portion towardthe center of the predetermined region 73. The end regions 73A includethe end region 73A that includes the end portion on one side of thepredetermined region 73 and the end region 73A that includes the endportion on the other side of the predetermined region 73, with respectto the tire circumferential direction. The middle region 73B is theregion of the predetermined region 73 between the end region 73A on oneside and the end region 73A on the other side.

In the present embodiment, the end insertion holes 40A are the insertionholes 40 provided in the predetermined region 73 of the tread portion 3disposed closest to the end portions of the predetermined region 73 withrespect to the tire circumferential direction. In other words, among theinsertion holes 40 formed in the tire circumferential direction, theinsertion hole 40 located closest to the end portion on one side of thepredetermined region 73 and the insertion hole 40 located closest to theend portion on the other side of the predetermined region 73 are endinsertion holes 40A. Two end insertion holes 40A are formed in onepredetermined region 73.

The middle insertion holes 40B are the insertion holes 40 other than theend insertion holes 40A formed in the predetermined region 73 of thetread portion 3.

For example, in a configuration in which 32 insertion holes 40 areformed in one predetermined region 73, of the 32 insertion holes 40, twoare end insertion holes 40A and 30 are middle insertion holes 40B.

In the present embodiment, the first inner diameter D41 b, the secondinner diameter D42 b, and the length H40 b are the same for theplurality of middle insertion holes 40B (for example, 30).

As described above, according to the present embodiment, cracking in aregion around the insertion holes 40 formed in the tread rubber 15 canbe suppressed. As a result, a decrease in the holding force of the studpins 30 provided by the insertion holes 40 and spoiling of theappearance of the studded tire 1, which are caused by such cracking, canbe prevented. Thus, a decrease in the performance of the studded tire 1is prevented.

In the present embodiment, the stud pins 30 include the body portion 31and the bottom flange portion 32. Thus, the stud pins 30 aresufficiently prevented from falling out of the insertion holes 40.

Note that in the embodiment described above, the end mold pins 60A aredefined as the mold pins 60 provided in the sector mold 51 that arelocated closest to the end portions of the sector mold 51 with respectto the tire circumferential direction. However, mold pins 60 provided onthe inner surface 53 within a predetermined range (for example, 5 cm)from the end portion of the inner surface 53 may also be defined as endmold pins 60A. In such an embodiment, three or more end mold pins 60Acan be provided in one sector mold 51.

Note that in the embodiment described above, the end insertion holes 40Aare defined as the insertion holes 40 provided in the tread portion 3disposed closest to the boundary portion 70 in the tire circumferentialdirection. However, insertion holes 40 formed within a predeterminedrange (for example, 5 cm) from the boundary portion 70 may also bedefined as end insertion holes 40A. In such an embodiment, three or moreend insertion holes 40A can be formed in one predetermined region 73.

Second Embodiment

A second embodiment will now be described. In the followingdescriptions, constituents identical to those in the above-describedembodiments have the same reference signs, and descriptions thereof willbe simplified or omitted.

FIG. 11 is a diagram schematically illustrating an example of the treadportion 3 according to the present embodiment. As illustrated in FIG.11, the tread portion 3 includes a first region AR1 on one side of theequator line CL in the tire lateral direction and a second region AR2 onthe other side. The insertion holes 40 are formed in the first regionAR1 and the second region AR2.

The sector molds 51 include the mold pins 60 for forming the insertionholes 40 in the first region AR1 and the mold pins 60 for forming theinsertion holes 40 in the second region AR2. The sector molds 51 formthe insertion holes 40 illustrated in FIG. 11.

Of the insertion holes 40 formed in the first region AR1, the insertionhole 40 located closest to the boundary portion 70, which is the endportion of the predetermined region 73, in the tire circumferentialdirection may be defined as the end insertion hole 40A. Of the insertionholes 40 formed in the second region AR2, the insertion hole 40 locatedclosest to the boundary portion 70, which is the end portion of thepredetermined region 73, in the tire circumferential direction may bedefined as the end insertion hole 40A.

In the example illustrated in FIG. 11, an insertion hole 401, aninsertion hole 402, and an insertion hole 403 are formed in thepredetermined region 73. The insertion hole 401 and the insertion hole402 are formed in the first region AR1 of the predetermined region 73.The insertion hole 403 is formed in the second region AR2 of thepredetermined region 73. The insertion hole 401 is located closest tothe boundary portion 70, the insertion hole 402 is located closest tothe boundary portion 70 after the insertion hole 401, and the insertionhole 403 is located farthest from the boundary portion 70.

In the first region AR1, the insertion hole 401 is located closest tothe boundary portion 70 and is thus defined as an end insertion hole40A. The insertion hole 403 is located further away from the boundaryportion 70 than the insertion hole 402. However, the insertion hole 403is located closest to the boundary portion 70 of the insertion holes 40formed in the second region AR2. Accordingly, the insertion hole 403 isdefined as an end insertion hole 40A. The insertion hole 402 is definedas a middle insertion hole 40B.

The insertion hole 401 (end insertion hole 40A) is formed by the moldpin 60 located closest to the end portion of the inner surface 53 of thesector mold 51 in the tire circumferential direction of the mold pins 60for forming the insertion holes 40 in the first region AR1. Theinsertion hole 403 (end insertion hole 40A) is formed by the mold pin 60located closest to the end portion of the inner surface 53 of the sectormold 51 in the tire circumferential direction of the mold pins 60 forforming the insertion holes 40 in the second region AR2.

As described above, in the present embodiment, the stud pins 30 areprevented from falling out from the first region AR1 and the secondregion AR2. Thus, a decrease in the running performance of the studdedtire 1 is suppressed.

Note that in the first embodiment and the second embodiment, the moldpins 60 are classified into two types: the end mold pins 60A and themiddle mold pins 60B. This configuration minimizes the types of moldpins 60 to allow the mold 50 to be easily manufactured, which suppressesan increase in the cost of the mold 50. Note that the sector molds 51may be provided with three or more types of mold pins 60 with varyingfirst outer diameters D61 of the trunk portion 61. In embodiments inwhich three or more mold pins 60 with varying first outer diameters D61of the trunk portion 61 are disposed in the tire circumferentialdirection, a plurality of mold pins 60 may be provided with the firstouter diameter D61 of the mold pins 60 gradually increasing from thecentral portion to the end portion of the inner surface 53.

Examples

FIG. 12 is a table showing results of evaluation tests for studded tires1 according to the embodiments of the present technology. FIG. 12 showsresults of evaluation tests which involved finding the number ofinsertion holes 40 around which cracking occurred (number of cracks) outof the insertion holes 40 formed in the studded tire 1.

Tires 1B with a tire size of 205/55R16 were vulcanization molded usingthe mold 50. Thereafter, the sector molds 51 of the mold 50 were movedto release the tire 1B. The number of cracks formed around the insertionholes 40 when the mold pins 60 were removed from the insertion holes 40was counted. Note that 20 tires 1B were vulcanization molded. Onehundred twenty insertion holes 40 were formed in each tire 1B. In eachtire 1B, the number of insertion holes 40 disposed near the boundaryportion 70 was 32. Thus, the total number of insertion holes 40 disposednear the boundary portion 70 was 640 (32×20).

Conventional example in FIG. 12 refers to an example in which the moldpins 60 provided on the sector molds 51 all have the same dimensions.Example 1, Example 2, and Example 3 are examples in which the mold pins60 provided on the sector molds 51 include end mold pins 60A and middlemold pins 60B. In Example 1, the first outer diameter D61 a of the endmold pins 60A is 0.3 mm greater than the first outer diameter D61 b ofthe middle mold pins 60B. In Example 2, in addition to the conditions ofExample 1, the second outer diameter D62 a of the end mold pins 60A is0.5 mm less than the second outer diameter D62 b of the middle mold pins60B. In Example 3, in addition to the conditions of Example 2, thelength H60 a of the end mold pins 60A is 0.2 mm less than the length H60b of the middle mold pins 60B.

As shown in FIG. 12, for the conventional example, cracking was found ina region around 30 insertion holes 40 out of the 640 insertion holes 40.For Example 1, cracking was found in a region around ten insertion holes40 out of the 640 insertion holes 40. For Example 2, cracking was foundin a region around seven insertion holes 40 out of the 640 insertionholes 40. For Example 3, cracking was found in a region around threeinsertion holes 40 out of the 640 insertion holes 40.

This shows that providing the sector molds 51 with the end mold pins 60Aand the middle mold pins 60B can suppress cracking.

1. A tire mold for forming a tire that includes insertion holes intowhich stud pins are inserted, the tire mold comprising: a plurality ofsector molds for forming a tread portion of the tire, the plurality ofsector molds being disposed in a tire circumferential direction; and aplurality of mold pins for forming the insertion holes in the treadportion, the plurality of mold pins being provided on inner surfaces ofthe plurality of sector molds that oppose the tread portion andprojecting inward in a tire radial direction; the stud pins eachcomprising a body portion and a bottom flange portion; the insertionholes each comprising a first hole portion with a first inner diameterwhere the body portion of the stud pin is disposed and a second holeportion with a second inner diameter greater than the first innerdiameter where the bottom flange portion of the stud pin is disposed;the plurality of mold pins each comprising a trunk portion with a firstouter diameter for forming the first hole portion and a tip portion witha second outer diameter greater than the first outer diameter forforming the second hole portion; and the first outer diameter of thetrunk portion of an end mold pin of the plurality of mold pins providedin an end region in the tire circumferential direction of each of theplurality of sector molds being greater than the first outer diameter ofthe trunk portion of a middle mold pin of the plurality of mold pinsprovided in a middle region of each of the plurality of sector molds,the middle region being located between the end region on one side andthe end region on another side in the tire circumferential direction. 2.The tire mold according to claim 1, wherein a difference between thefirst outer diameter of the end mold pin and the first outer diameter ofthe middle mold pin is from 0.1 mm to 1.0 mm.
 3. The tire mold accordingto claim 1, wherein the second outer diameter of the tip portion of theend mold pin is less than the second outer diameter of the tip portionof the middle mold pin.
 4. The tire mold according to claim 3, wherein adifference between the second outer diameter of the end mold pin and thesecond outer diameter of the middle mold pin is from 0.2 mm to 1.5 mm.5. The tire mold according to claim 1, wherein a length of the end moldpin is less than a length of the middle mold pin.
 6. The tire moldaccording to claim 5, wherein a difference between the length of the endmold pin and the length of the middle mold pin is from 0.1 mm to 1.0 mm.7. The tire mold according to claim 1, wherein the end mold pin is amold pin of the plurality of mold pins provided on each of the pluralityof sector molds located closest to an end portion of the sector mold inthe tire circumferential direction.
 8. The tire mold according to claim1, wherein the tread portion comprises a first region on one side of anequator line of the tire in a tire lateral direction and a second regionon another side, the plurality of mold pins comprise a plurality of moldpins for forming the insertion holes in the first region and a pluralityof mold pins for forming the insertion holes in the second region, andthe end mold pin is a mold pin of the plurality of mold pins for formingthe insertion holes in the first region and the second region locatedclosest to an end portion of each of the plurality of sector molds inthe tire circumferential direction.
 9. The tire mold according to claim1, wherein the middle mold pin is a mold pin of the plurality of moldpins provided on the plurality of sector molds other than the end moldpins, and the first outer diameter, the second outer diameter, and alength are the same for all of the middle mold pins.
 10. A pneumatictire, comprising: a tread portion formed by a plurality of sector moldsdisposed in a tire circumferential direction; a plurality of insertionholes into which stud pins are inserted, the plurality of insertionholes being formed in the tread portion by mold pins provided on innersurfaces of the plurality of sector molds that oppose the tread portionand projecting inward in a tire radial direction; the stud pins eachcomprising a body portion and a bottom flange portion; the plurality ofinsertion holes each comprising a first hole portion with a first innerdiameter where the body portion of the stud pin is disposed and a secondhole portion with a second inner diameter greater than the first innerdiameter where the bottom flange portion of the stud pin is disposed;and the first inner diameter of the first hole portion of an endinsertion hole of the plurality of insertion holes formed in an endregion in the tire circumferential direction of a predetermined region,which is formed by one of the plurality of sector molds, of the treadportion being greater than the first inner diameter of the first holeportion of a middle insertion hole of the plurality of insertion holesformed in a middle region of the tread portion, the middle region beinglocated between the end region on one side and the end region on anotherside in the tire circumferential direction.
 11. The pneumatic tireaccording to claim 10, wherein a difference between the first innerdiameter of the end insertion hole and the first inner diameter of themiddle insertion hole is from 0.1 mm to 1.0 mm.
 12. The pneumatic tireaccording to claim 10, wherein the second inner diameter of the secondhole portion of the end insertion hole is less than the second innerdiameter of the second hole portion of the middle insertion hole. 13.The pneumatic tire according to claim 12, wherein a difference betweenthe second inner diameter of the end insertion hole and the second innerdiameter of the middle insertion hole is from 0.2 mm to 1.5 mm.
 14. Thepneumatic tire according to claim 10, wherein a length of the endinsertion hole is less than a length of the middle insertion hole. 15.The pneumatic tire according to claim 14, wherein a difference betweenthe length of the end insertion hole and the length of the middleinsertion hole is from 0.1 mm to 1.0 mm.
 16. The pneumatic tireaccording to claim 10, wherein the end insertion hole is an insertionhole of the plurality of insertion holes provided in the predeterminedregion located closest to an end portion of the predetermined region inthe tire circumferential direction.
 17. The pneumatic tire according toclaim 10, wherein the tread portion comprises a first region on one sideof a tire equator line in a tire lateral direction and a second regionon another side, the plurality of insertion holes are formed in thefirst region and the second region, and the end insertion hole is aninsertion hole of the plurality of insertion holes formed in the firstregion located closest to an end portion of the predetermined region inthe tire circumferential direction and is an insertion hole of theplurality of insertion holes formed in the second region located closestto an end portion of the predetermined region in the tirecircumferential direction.
 18. The pneumatic tire according to claim 10,wherein the middle insertion hole is an insertion hole of the pluralityof insertion holes provided in the tread portion other than end moldpins, and the first inner diameter, the second inner diameter, and alength are the same for all of the middle insertion holes.